Producing semi-crystalline pulverulent polycarbonate and use thereof in additive manufacturing

ABSTRACT

Ways of preparing a partially crystalline polycarbonate powder are provided that include dissolving an amorphous polycarbonate in a polar aprotic solvent to form a first solution of solubilized polycarbonate at a first temperature. The first solution is then cooled to a second temperature, the second temperature being lower than the first temperature, where a portion of the solubilized polycarbonate precipitates from the first solution to form a second solution including the partially crystalline polycarbonate powder. Certain partially crystalline polycarbonate powders resulting from such methods are particularly useful in additive manufacturing processes, including powder bed fusion processes.

FIELD

The present technology relates to precipitating a pulverulentpolycarbonate in a solvent, allowing the pulverulent polycarbonate toform crystallites, and employing the precipitated pulverulentpolycarbonate in a powder-based additive manufacturing process.

BACKGROUND OF THE INVENTION

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Various additive manufacturing processes, also known asthree-dimensional (3D) printing processes, can be used to formthree-dimensional objects by fusing certain materials at particularlocations and/or in layers. Material can be joined or solidified undercomputer control, for example working from a computer-aided design (CAD)model, to create a three-dimensional object, with material being addedtogether, such as liquid molecules or powder grains being fusedtogether, typically layer-by-layer. Various types of additivemanufacturing include binder jetting, directed energy deposition,material extrusion, material jetting, powder bed fusion, sheetlamination, and vat photopolymerization.

Certain additive manufacturing methods can be conducted usingthermoplastic polymers (e.g., polycarbonate), which include materialextrusion, fused deposition modeling, and powder bed fusion. Powder bedfusion, in general, involves selective fusing of materials in a powderbed. The method can fuse parts of a layer of powder material, moveupward in a working area, add another layer of powder material, andrepeat the process until an object is built up therefrom. The powder bedfusion process can use unfused media to support overhangs and thin wallsin the object being produced, which can reduce the need for temporaryauxiliary supports in forming the object. In selective heat sintering, athermal printhead can apply heat to layers of powdered thermoplastic;when a layer is finished, the powder bed moves down, and an automatedroller adds a new layer of material which is sintered to form the nextcross-section of the object. Selective laser sintering is another powderbed fusion process that can use one or more lasers to fuse powderedthermoplastic polymers into the desired three-dimensional object.

Materials for powder bed fusion processes preferably have a uniformshape, size, and composition. The preparation of such powders fromthermoplastic polymers on an economical and large scale is notstraightforward. What is more, it can be difficult to use amorphouspolycarbonates, particularly in powder bed fusing processes such asselective laser sintering, because such polycarbonates may not exhibit asharp melting point. This property can result in dissipation of theapplied thermal energy source (e.g., a laser beam) into the regionssurrounding where the energy source contacts or strikes the powder bed.This undesired dissipation of thermal energy can result in unstableprocessing as well as poor feature resolution in the intendedthree-dimensional object being produced.

Certain preparations of polycarbonate powders for powder bed fusion areknown. For example, U.S. Pub. No. 2017/9567443 B2, Japanese Pat. No.2017/095650 A, and U.S. Pub. No. 2018/0244863 A1 each discuss methodsthat include dissolving polycarbonate in a suitable organic solvent,addition of a dispersing polymer to promote and sustain emulsionformation, and addition of a solvent that is miscible with the organicsolvent but that is not a solvent for the polycarbonate, resulting inemulsion formation and subsequent precipitation of polycarbonate powder.In addition, WO 2018/071578 A1 and U.S. Pub. No. 2018/0178413 A1describe the use of solvents to induce crystalline domain formation inpre-formed powder particles produced from grinding methods.

Such methods of preparing crystalline polycarbonate powders for use inpowder bed fusion processes still present several technical issues. Inparticular, prior methods of processing polycarbonate powder into a formsuitable for use in certain methods, such as selective laser sintering(SLS), multi jet fusion (MJF), high speed sintering (HSS), andelectrophotographic 3D-printing applications, can require the use ofmixed solvents and dispersants. There is accordingly a need to provide asingle solvent method, facilitating solvent recovery and reuse, that canform polycarbonate powder having optimal crystallinity and optimalparticle size distribution from amorphous polymer, where the crystallinepolycarbonate powder results in improved powder bed fusion performance.

SUMMARY OF THE INVENTION

The present technology includes processes, compositions, and articles ofmanufacture that relate to preparation of a partially crystallinepolycarbonate powder and use thereof in additive manufacturingprocesses, including powder bed fusion processes.

Methods of preparing a partially crystalline polycarbonate powder areprovided that include dissolving an amorphous polycarbonate in a polaraprotic solvent to form a first solution of solubilized polycarbonate ata first temperature. The first solution is then cooled to a secondtemperature, where the second temperature is lower than the firsttemperature. A portion of the solubilized polycarbonate precipitatesfrom the first solution to form a second solution including thepartially crystalline polycarbonate powder. Powder compositions for usein powder bed fusion processes are provided that include a partiallycrystalline polycarbonate powder prepared by such methods. Objects canbe prepared by using such partially crystalline polycarbonate powders ina powder bed fusion process to form the object.

The disclosed exemplary apparatuses, systems, and methods provide powderpolycarbonate having a suitable operating window for use in SLS, MJF,HSS, and electrophotography 3D-printing applications. An embodiment ofthe disclosure may provide a precipitated pulverulent polycarbonateformed through precipitating the polycarbonate in a solvent, allowingthe polymer to form crystallites, and then employing the precipitatedpulverulent polycarbonate in a powder-based 3D-printing process.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and are not intended to limit the scope of thepresent disclosure.

FIG. 1 : Low vacuum secondary electron detector (LVSED) scanningelectron micrograph (SEM) of pulverulent polycarbonate as produced byExample 1, magnification 50×.

FIG. 2 : Low vacuum secondary electron detector (LVSED) scanningelectron micrograph (SEM) of pulverulent polycarbonate as produced byExample 1, magnification 500×.

FIG. 3 : Differential scanning calorimetry (DSC) of pulverulentpolycarbonate as produced by Example 1.

FIG. 4 : Selective laser sintering (SLS) process to produce samplecoupon from pulverulent polycarbonate as described in Example 1.

FIG. 5 : Selective laser sintering (SLS) process to produce sampletensile bars from pulverulent polycarbonate as described in Example 3.

FIG. 6 : Selective laser sintered (SLS) 1×1×1-inch cubed object printedfrom pulverulent polycarbonate as described in Example 3. Sides werepolished to remove exterior powder coating and expose the interior ofthe part.

DETAILED DESCRIPTION

The following description of technology is merely exemplary in nature ofthe subject matter, manufacture and use of one or more inventions, andis not intended to limit the scope, application, or uses of any specificinvention claimed in this application or in such other applications asmay be filed claiming priority to this application, or patents issuingtherefrom. Regarding methods disclosed, the order of the steps presentedis exemplary in nature, and thus, the order of the steps can bedifferent in various embodiments. “A” and “an” as used herein indicate“at least one” of the item is present; a plurality of such items may bepresent, when possible. Except where otherwise expressly indicated, allnumerical quantities in this description are to be understood asmodified by the word “about” and all geometric and spatial descriptorsare to be understood as modified by the word “substantially” indescribing the broadest scope of the technology. “About” when applied tonumerical values indicates that the calculation or the measurementallows some slight imprecision in the value (with some approach toexactness in the value; approximately or reasonably close to the value;nearly). If, for some reason, the imprecision provided by “about” and/or“substantially” is not otherwise understood in the art with thisordinary meaning, then “about” and/or “substantially” as used hereinindicates at least variations that may arise from ordinary methods ofmeasuring or using such parameters.

All documents, including patents, patent applications, and scientificliterature cited in this detailed description are incorporated herein byreference, unless otherwise expressly indicated. Where any conflict orambiguity may exist between a document incorporated by reference andthis detailed description, the present detailed description controls.

Although the open-ended term “comprising,” as a synonym ofnon-restrictive terms such as including, containing, or having, is usedherein to describe and claim embodiments of the present technology,embodiments may alternatively be described using more limiting termssuch as “consisting of” or “consisting essentially of.” Thus, for anygiven embodiment reciting materials, components, or process steps, thepresent technology also specifically includes embodiments consisting of,or consisting essentially of, such materials, components, or processsteps excluding additional materials, components or processes (forconsisting of) and excluding additional materials, components orprocesses affecting the significant properties of the embodiment (forconsisting essentially of), even though such additional materials,components or processes are not explicitly recited in this application.For example, recitation of a composition or process reciting elements A,B and C specifically envisions embodiments consisting of, and consistingessentially of, A, B and C, excluding an element D that may be recitedin the art, even though element D is not explicitly described as beingexcluded herein.

As referred to herein, disclosures of ranges are, unless specifiedotherwise, inclusive of endpoints and include all distinct values andfurther divided ranges within the entire range. Thus, for example, arange of “from A to B” or “from about A to about B” is inclusive of Aand of B. Disclosure of values and ranges of values for specificparameters (such as amounts, weight percentages, etc.) are not exclusiveof other values and ranges of values useful herein. It is envisionedthat two or more specific exemplified values for a given parameter maydefine endpoints for a range of values that may be claimed for theparameter. For example, if Parameter X is exemplified herein to havevalue A and also exemplified to have value Z, it is envisioned thatParameter X may have a range of values from about A to about Z.Similarly, it is envisioned that disclosure of two or more ranges ofvalues for a parameter (whether such ranges are nested, overlapping ordistinct) subsume all possible combination of ranges for the value thatmight be claimed using endpoints of the disclosed ranges. For example,if Parameter X is exemplified herein to have values in the range of1-10, or 2-9, or 3-8, it is also envisioned that Parameter X may haveother ranges of values including 1-9, 1-8, 1-3, 1-2, 2-10, 2-8, 2-3,3-10, 3-9, and so on.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to” or “directly coupled to” another element orlayer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

The present technology provides ways to make and use partiallycrystalline polycarbonate powder, including partially crystallinepolycarbonate powder having suitable characteristics for use inselective laser sintering (SLS), multi jet fusion (MJF), high speedsintering (HSS), and electrophotographic 3D-printing. Embodimentsprovide a precipitated pulverulent polycarbonate formed throughprecipitating the polycarbonate in a solvent, allowing the polymer toform crystallites, and then employing the precipitated pulverulentpolycarbonate in a powder-based 3D-printing process. The presentpartially crystalline polycarbonate powder exhibits optimizedcharacteristics for powder bed fusion processes, including optimizedparticle size, shape, distribution, and crystallinity, while at the sametime using a dispersant-free single-solvent process in manufacturethereof.

Methods of preparing a partially crystalline polycarbonate powder caninclude dissolving an amorphous polycarbonate in a polar aprotic organicsolvent to form a solution at elevated temperature; cooling the solutionto room temperature to form a pulverulent, partially crystallinepolycarbonate precipitate having a D₉₀ particle size of less than 150μm; an average particle diameter of less than or equal to 100 μm, or anaverage particle diameter of between 0 to 100 μm; and at least 20%crystallinity, or at least 25% crystallinity, or 25 to 35%crystallinity. Prior methods of processing polycarbonate powder into aform suitable for use in an additive manufacturing process, such asselective laser sintering (SLS), multi jet fusion (MJF), high speedsintering (HSS), and electrophotographic 3D-printing applications, thatrequire the use of mixed solvents and dispersants; whereas, theprocesses described herein can employ a single solvent method,facilitating solvent recovery and reuse. The methods also yield aproduct where the particles can exhibit a certain size (about 30micrometers (μm) to about 40 μm in average diameter), low dispersity,spheroidal shape, and crystalline character suitable for theabove-mentioned printing processes in comparison to the results ofaforementioned processes.

In certain embodiments, methods of preparing a partially crystallinepolycarbonate powder are provided. Such methods can include dissolvingan amorphous polycarbonate in a polar aprotic solvent to form a firstsolution of solubilized polycarbonate at a first temperature. The firstsolution is then cooled to a second temperature, the second temperaturebeing lower than the first temperature, where a portion of thesolubilized polycarbonate precipitates from the first solution to form asecond solution including the partially crystalline polycarbonatepowder. The precipitated partially crystalline polycarbonate powder canbe separated from a remainder of the second solution. The separatedpartially crystalline polycarbonate powder can also be dried. It ispossible to repeat the dissolving step using the remainder of the secondsolution as the polar aprotic solvent, and further repeat the coolingstep to form the second solution including another partially crystallinepolycarbonate powder. In certain embodiments, the polar aprotic solventcan include dimethyl sulfoxide (DMSO), diphenyl ether, anisole orcombination thereof.

Various temperatures can be employed in methods of preparing thepartially crystalline polycarbonate powder. The dissolving step caninclude heating the amorphous polycarbonate in the polar aprotic solventto form the first solution of solubilized polycarbonate at the firsttemperature, where the first temperature is greater than roomtemperature. The cooling step can include cooling the first solution tothe second temperature, where the second temperature is roomtemperature. In certain embodiments, the first solution can be saturatedwith polycarbonate at the first temperature. For example, the firstsolution can be saturated with polycarbonate at the first temperature incomparison to the solubility limit of polycarbonate in the firstsolution at the second temperature.

Various embodiments of the partially crystalline polycarbonate powderprepared according to the present methods can exhibit the followingphysical characteristics. The partially crystalline polycarbonate powdercan have a D₉₀ particle size of less than about 150 μm; i.e., 90 vol %of the particles in the total distribution of the partially crystallinepolycarbonate powder have a particle diameter of 150 μm or smaller. Incertain embodiments, the partially crystalline polycarbonate powder canhave an average particle diameter of less than about 100 μm. Thepartially crystalline polycarbonate powder can also have an averageparticle diameter from about 1 μm to about 100 μm. Particularembodiments include where the partially crystalline polycarbonate powderhas an average particle diameter from about 30 μm to about 40 μm. Thepartially crystalline polycarbonate powder can be in the form ofspheroidal particles. Various crystallinity values are possible, wherethe partially crystalline polycarbonate powder can have at least about20% crystallinity, at least about 25% crystallinity, and in certainembodiments the partially crystalline polycarbonate powder can have acrystallinity between about 25% and about 35%.

In certain embodiments, powder compositions for use in a powder bedfusion process are provided, where such powder compositions include apartially crystalline polycarbonate powder prepared according to themethods provided herein. For example, a powder composition for use in apowder bed fusion process can include a partially crystallinepolycarbonate powder having a D₉₀ particle size of less than about 150μm, an average particle diameter from about 30 μm to about 40 μm, and acrystallinity between about 25% and about 35%. Such powder compositionscan include mixtures of partially crystalline polycarbonate powdershaving different physical characteristics as well as additives and othercomponents as described herein.

In certain embodiments, methods of preparing an object are provided.Such methods can include preparing a partially crystalline polycarbonatepowder by a method that includes dissolving an amorphous polycarbonatein a polar aprotic solvent to form a first solution of solubilizedpolycarbonate at a first temperature. The first solution can then becooled to a second temperature, the second temperature being lower thanthe first temperature, wherein a portion of the solubilizedpolycarbonate precipitates from the first solution to form a secondsolution including the partially crystalline polycarbonate powder. Thepartially crystalline polycarbonate powder is then used in a powder bedfusion process to form the object. Certain methods of preparing anobject include providing a partially crystalline polycarbonate powderhaving a D₉₀ particle size of less than about 150 μm, an averageparticle diameter from about 30 μm to about 40 μm, and a crystallinitybetween about 25% and about 35%. The partially crystalline polycarbonatepowder is then used in a powder bed fusion process to form the object.

In certain embodiments, one or more objects prepared by an additivemanufacturing process are provided. Such methods can include providing apartially crystalline polycarbonate powder prepared according to one ormore of the methods described herein. The partially crystallinepolycarbonate powder is then used in a powder bed fusion process to formthe one or more objects.

In certain embodiments, the present technology includes methods ofconverting an amorphous polycarbonate to a partially crystallinepolycarbonate powder. Such methods can include dissolving the amorphouspolycarbonate in a suitable polar aprotic solvent such as DMSO, anisole,or diphenyl ether, to form a solution at an elevated temperature aboveroom temperature, subsequently cooling the solution to room temperatureto form a partially crystalline polycarbonate precipitate, andrecovering the partially crystalline polycarbonate precipitate as asubstantially uniform polycarbonate powder from the solvent. Theresulting partially crystalline polycarbonate powder can have goodcrystallinity, particle size distribution, and flowability. Inparticular, the partially crystalline polycarbonate powder can include:a D₉₀ particle size of less than 150 μm; an average particle diameter ofless than or equal to 100 μm or an average particle diameter of between0 to 100 μm; and at least 20% crystallinity, at least 25% crystallinity,or 25 to 35% crystallinity. As the majority of the particles of thepartially crystalline polycarbonate powder can have a size of less than150 μm, the partially crystalline polycarbonate powder can therefore beeffectively used in powder bed fusion processes, e.g., selective lasersintering processes, to produce layers having a thickness of 100 μm to150 μm.

In certain embodiments, the present technology includes methods forpowder bed fusing a powder composition including the partiallycrystalline polycarbonate powder to form a three-dimensional object. Dueto the good flowability of the partially crystalline polycarbonatepowder, a smooth and dense powder bed can be formed allowing for optimumprecision and density of the sintered object. The partially crystallinenature of the polycarbonate material further allows for ease ofprocessing, where the use of crystalline polycarbonate permits the useof reduced melting energy versus the melting of corresponding amorphouspolymeric materials.

The terms “amorphous” and “crystalline” as used herein refer their usualmeanings in the polymer art, with respect to alignment of polymermolecular chains. For example, in an amorphous polymer (e.g.,polycarbonate) the molecules can be oriented randomly and can beintertwined, much like cooked spaghetti noodles, and the polymer canhave a glasslike, transparent appearance. In crystalline polymers, thepolymer molecules can be aligned together in ordered regions, much likeuncooked spaghetti noodles. In the polymer art, some types ofcrystalline polymers are sometimes referred to as “semi-crystallinepolymers.” The term “crystalline” as used herein refers to bothcrystalline and semi-crystalline polymers. The term “partiallycrystalline polycarbonate” as used herein means a portion of thepolycarbonate polymer is in crystalline form. The term “percentcrystallinity” or “% crystallinity” as used herein, refers to theportion of the amorphous polymer that has been converted to thepartially crystalline form. The percentage is based upon the totalweight of the partially crystalline polymer.

The particle size and shape of the partially crystalline polymer canaffect its use in additive manufacturing processes. In regards toparticle size, as used herein, D₅₀ (as known as “average particlediameter”) refers to the particle diameter of the powder where 50 vol. %of the particles in the total distribution of the referenced sample havethe noted particle diameter or smaller. Similarly, D₁₀ refers to theparticle diameter of the powder where 10 vol. % of the particles in thetotal distribution of the referenced sample have the noted particlediameter or smaller; D₉₀ refers to the particle diameter of the powderwhere 90 vol. % of the particles in the total distribution of thereferenced sample have the noted particle diameter or smaller; and D₉₅refers to the particle diameter of the powder where 95 vol. % of theparticles in the total distribution of the referenced sample have thenoted particle diameter or smaller.

In terms of particle shape, and in particular particle roundness, whichaids in flowability, and as derived from micrograph images of individualparticles, may be expressed in terms of circular character, orcircularity, where individual particle circularity is defined as the 4πA/P², where A is the area of the particle and P is the perimeter lengthof the particle, both as viewed from a random perspective. Sphericity, arelated parameter, is derived as the square root of circularity.Circularity is a numerical value greater than zero and less than orequal to one. A perfectly circular particle is referred to as having acircularity of 1.00. Tables of population circularity data arerepresented in such a way that various levels of circularity (e.g.,0.65, 0.75, 0.85, 0.90, and 0.95) are accompanied by percentages of theparticle sample population with a circularity greater than the tabulatedvalue. Particle size and shape can be measured by any suitable methodsknown in the art to measure particle size by diameter. In someembodiments, the particle size and shape are determined by laserdiffraction as is known in the art. For example, particle size can bedetermined using a laser diffractometer such as the Microtrac S3500 withstatic image analysis accessory using PartAnSI software to analyze thecaptured images of the particles. The partially crystallinepolycarbonate powder provided herein can have a D₉₀ particle size ofless than 150 μm and has a D₁₀ of at least 10 μm or 20 μm.

The term “high shear mixing conditions” refers to methods of agitatingthe components in a mixture (e.g., liquid mixture) under conditions inwhich high shear forces are generated. As is known in the art, a highshear mixer creates patterns of flow and turbulence, generally using animpeller that rotates inside a stator. Once the impeller has drawnmixture in, it subjects the mixture sudden changes of direction andacceleration, often approaching 90 degrees, such that the mixturecontacts the wall of the stator with centrifugal force, or is forcedthrough the holes in the stator at great pressure and speed, in a finaldisintegrating change of direction and acceleration. In certainembodiments of high shear mixing conditions, the high shear mixingcomprises mixing at speeds of 2,000 rotations per minute (rpm) to 20,000rpm, specifically, 3,000 rpm to 15,000 rpm, more specifically 4,000 rpmto 10,000 rpm. High shear mixing can be achieved with any commerciallyavailable high shear mixers. For example, a high shear mixer such as aSilverson L5M homogenizer can be used.

The term “powder bed fusing” or “powder bed fusion” is used herein tomean processes wherein the polycarbonate is selectively sintered ormelted and fused, layer-by-layer to provide a 3-D object. Sintering canresult in objects having a density of less than about 90% of the densityof the solid powder composition, whereas melting can provide objectshaving a density of 90%-100% of the solid powder composition. Use ofcrystalline polycarbonate as provided herein can facilitate melting suchthat resulting densities can approach densities achieved by injectionmolding methods.

Powder bed fusing or powder bed fusion further includes all lasersintering and all selective laser sintering processes as well as otherpowder bed fusing technologies as defined by ASTM F2792-12a. Forexample, sintering of the powder composition can be accomplished viaapplication of electromagnetic radiation other than that produced by alaser, with the selectivity of the sintering achieved, for example,through selective application of inhibitors, absorbers, susceptors, orthe electromagnetic radiation (e.g., through use of masks or directedlaser beams). Any other suitable source of electromagnetic radiation canbe used, including, for example, infrared radiation sources, microwavegenerators, lasers, radiative heaters, lamps, or a combination thereof.In certain embodiments, selective mask sintering (“SMS”) techniques canbe used to produce three-dimensional objects. For further discussion ofSMS processes, see for example U.S. Pat. No. 6,531,086, which describesan SMS machine in which a shielding mask is used to selectively blockinfrared radiation, resulting in the selective irradiation of a portionof a powder layer. If using an SMS process to produce objects frompowder compositions of the present technology, it can be desirable toinclude one or more materials in the powder composition that enhance theinfrared absorption properties of the powder composition. For example,the powder composition can include one or more heat absorbers ordark-colored materials (e.g., carbon black, carbon nanotubes, or carbonfibers).

Also included herein are all three-dimensional objects made by powderbed fusing compositions including the partially crystallinepolycarbonate powder described herein. After a layer-by-layermanufacture of an object, the object can exhibit excellent resolution,durability, and strength. Such objects can include various articles ofmanufacture that have a wide variety of uses, including uses asprototypes, as end products, as well as molds for end products.

In particular, powder bed fused (e.g., laser sintered) objects can beproduced from compositions including the partially crystallinepolycarbonate powder using any suitable powder bed fusing processesincluding laser sintering processes. These objects can include aplurality of overlying and adherent sintered layers that include apolymeric matrix which, in some embodiments, can have reinforcementparticles dispersed throughout the polymeric matrix. Laser sinteringprocesses are known and are based on the selective sintering of polymerparticles, where layers of polymer particles are briefly exposed tolaser light and the polymer particles exposed to the laser light arethus bonded to one another. Successive sintering of layers of polymerparticles produces three-dimensional objects. Details concerning theselective laser sintering process are found, by way of example, in thespecifications of U.S. Pat. No. 6,136,948 and WO 96/06881. However, thepartially crystalline polycarbonate powder described herein can also beused in other rapid prototyping or rapid manufacturing processing of theprior art, in particular in those described above. For example, thepartially crystalline polycarbonate powder can in particular be used forproducing moldings from powders via the SLS (selective laser sintering)process, as described in U.S. Pat. No. 6,136,948 or WO 96/06881, via theSIB process (selective inhibition of bonding of powder), as described inWO 01/38061, via 3D printing, as described in EP 0 431 924, or via amicrowave process, as described in DE 103 11 438.

In certain embodiments, the present technology includes forming aplurality of layers in a preset pattern by an additive manufacturingprocess. “Plurality” as used in the context of additive manufacturingcan include 5 or more layers, or 20 or more layers. The maximum numberof layers can vary greatly, determined, for example, by considerationssuch as the size of the object being manufactured, the technique used,the capacities and capabilities of the equipment used, and the level ofdetail desired in the final object. For example, 5 to 100,000 layers canbe formed, or 20 to 50,000 layers can be formed, or 50 to 50,000 layerscan be formed.

As used herein, “layer” is a term of convenience that includes anyshape, regular or irregular, having at least a predetermined thickness.In certain embodiments, the size and configuration two dimensions arepredetermined, and in certain embodiments, the size and shape of allthree-dimensions of the layer are predetermined. The thickness of eachlayer can vary widely depending on the additive manufacturing method. Incertain embodiments the thickness of each layer as formed can differfrom a previous or subsequent layer. In certain embodiments, thethickness of each layer can be the same. In certain embodiments thethickness of each layer as formed can be from 0.5 millimeters (mm) to 5mm.

An object can be formed from a preset pattern, which can be determinedfrom a three-dimensional digital representation of the desired object asis known in the art and as described herein. Material can be joined orsolidified under computer control, for example, working from acomputer-aided design (CAD) model, to create the three-dimensionalobject.

The fused layers of powder bed fused objects can be of any thicknesssuitable for selective laser sintered processing. The individual layerscan be each, on average, preferably at least 50 μm thick, morepreferably at least 80 μm thick, and even more preferably at least 100μm thick. In a preferred embodiment, the plurality of sintered layersare each, on average, preferably less than 500 μm thick, more preferablyless than 300 μm thick, and even more preferably less than 200 μm thick.Thus, the individual layers for some embodiments can be 50 to 500 μm, 80to 300 μm, or 100 to 200 μm thick. Three-dimensional objects producedfrom powder compositions of the present technology using alayer-by-layer powder bed fusing processes other than selective lasersintering can have layer thicknesses that are the same or different fromthose described above.

“Polycarbonate” as used herein means a polymer or copolymer havingrepeating structural carbonate units of formula (1):

wherein at least 60 percent of the total number of R¹ groups arearomatic, or each R¹ contains at least one C₆₋₃₀ aromatic group.Specifically, each R¹ can be derived from a dihydroxy compound such asan aromatic dihydroxy compound of formula (2) or a bisphenol of formula(3), as follows:

In formula (2), each R^(h) is independently a halogen atom, for examplebromine, a C₁₋₁₀ hydrocarbyl group such as a C₁₋₁₀ alkyl, ahalogen-substituted C₁₋₁₀ alkyl, a C₆₋₁₀ aryl, or a halogen-substitutedC₆₋₁₀ aryl, and n is 0 to 4.

In formula (3), R^(a) and R^(b) are each independently a halogen, C₁₋₁₂alkoxy, or C₁₋₁₂ alkyl, and p and q are each independently integers of 0to 4, such that when p or q is less than 4, the valence of each carbonof the ring is filled by hydrogen. In certain embodiments, p and q areeach 0, or p and q are each 1, and R^(a) and R^(b) are each a C₁₋₃ alkylgroup, specifically methyl, disposed meta to the hydroxy group on eacharylene group. X^(a) is a bridging group connecting the twohydroxy-substituted aromatic groups, where the bridging group and thehydroxy substituent of each C₆ arylene group are disposed ortho, meta,or para (specifically para) to each other on the C₆ arylene group, forexample, a single bond, —O—, —S—, —S(═O)—, —S(═O)₂— (e.g., bisphenol-Spolycarbonate, polysulfone), —C(═O)— (e.g., polyketone), or a C₁₋₁₈organic group, which can be cyclic or acyclic, aromatic or non-aromatic,and can further comprise heteroatoms such as halogens, oxygen, nitrogen,sulfur, silicon, or phosphorous. For example, X^(a) can be a substitutedor unsubstituted C₃₋₁₈ cycloalkylidene; a C₁₋₂₅ alkylidene of theformula —C(R^(c))(R^(d))— wherein R^(c) and R^(d) are each independentlyhydrogen, C₁₋₁₂ alkyl, C₁₋₁₂ cycloalkyl, C₇₋₁₂ arylalkyl, C₁₋₁₂heteroalkyl, or cyclic C₇₋₁₂ heteroarylalkyl; or a group of the formula—C(═R^(e))— wherein R^(e) is a divalent C₁₋₁₂ hydrocarbon group. Certainillustrative examples of dihydroxy compounds that can be used aredescribed, for example, in WO 2013/175448 A1, US 2014/0295363, and WO2014/072923.

Specific dihydroxy compounds include resorcinol,2,2-bis(4-hydroxyphenyl) propane (“bisphenol A” or “BPA”),3,3-bis(4-hydroxyphenyl) phthalimidine,2-phenyl-3,3′-bis(4-hydroxyphenyl) phthalimidine (also known as N-phenylphenolphthalein bisphenol, “PPPBP”, or3,3-bis(4-hydroxyphenyl)-2-phenylisoindolin-1-one),1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane, and1,1-bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyclohexane (isophoronebisphenol).

“Polycarbonate” as used herein also includes copolymers comprisingcarbonate units and ester units (“poly(ester-carbonate)s”, also known aspolyester-polycarbonates). Poly(ester-carbonate)s further contain, inaddition to recurring carbonate chain units of formula (1), repeatingester units of formula (4):

wherein J is a divalent group derived from a dihydroxy compound (whichincludes a reactive derivative thereof), and can be, for example, aC₂₋₁₀ alkylene, a C₆₋₂₀ cycloalkylene a C₆₋₂₀ arylene, or apolyoxyalkylene group in which the alkylene groups contain 2 to 6 carbonatoms, specifically, 2, 3, or 4 carbon atoms; and T is a divalent groupderived from a dicarboxylic acid (which includes a reactive derivativethereof), and can be, for example, a C₂₋₂₀ alkylene, a C₆₋₂₀cycloalkylene, or a C₆₋₂₀ arylene. Copolyesters containing a combinationof different T or J groups can be used. The polyester units can bebranched or linear.

Specific dihydroxy compounds include aromatic dihydroxy compounds offormula (2) (e.g., resorcinol), bisphenols of formula (3) (e.g.,bisphenol A), a C₁₋₈ aliphatic diol such as ethane diol, n-propane diol,i-propane diol, 1,4-butane diol, 1,6-cyclohexane diol,1,6-hydroxymethylcyclohexane, or a combination comprising at least oneof the foregoing dihydroxy compounds. Aliphatic dicarboxylic acids thatcan be used include C₆₋₂₀ aliphatic dicarboxylic acids (which includesthe terminal carboxyl groups), specifically linear C₈₋₁₂ aliphaticdicarboxylic acid such as decanedioic acid (sebacic acid); and alpha,omega-Ca dicarboxylic acids such as dodecanedioic acid (DDDA). Aromaticdicarboxylic acids that can be used include terephthalic acid,isophthalic acid, naphthalene dicarboxylic acid, 1,6-cyclohexanedicarboxylic acid, or a combination comprising at least one of theforegoing acids. A combination of isophthalic acid and terephthalic acidwherein the weight ratio of isophthalic acid to terephthalic acid is91:9 to 2:98 can be used.

Specific ester units include ethylene terephthalate units, n-propyleneterephthalate units, n-butylene terephthalate units, ester units derivedfrom isophthalic acid, terephthalic acid, and resorcinol (ITR esterunits), and ester units derived from sebacic acid and bisphenol A. Themolar ratio of ester units to carbonate units in thepoly(ester-carbonate)s can vary broadly, for example 1:99 to 99:1,specifically, 10:90 to 90:10, more specifically, 25:75 to 75:25, or from2:98 to 15:85.

The polycarbonates can have an intrinsic viscosity, as determined inchloroform at 25° C., of 0.3 to 1.5 deciliters per gram (dl/gm),specifically 0.45 to 1.0 dl/gm. The polycarbonates can have a weightaverage molecular weight of 5,000 to 200,000 Daltons, specifically15,000 to 100,000 Daltons, as measured by gel permeation chromatography(GPC), using a crosslinked styrene-divinylbenzene column and calibratedto polycarbonate references. GPC samples are prepared at a concentrationof 1 mg per mL (mg/mL) and are eluted at a flow rate of 1.5 mL perminute.

In certain embodiments, the method of preparing a partially crystallinepolycarbonate powder comprises dissolving an amorphous polycarbonate ina suitable polar aprotic solvent such as DMSO, anisole, or diphenylether, which is used as an illustration only with other suitablesolvents described herein (e.g., para.0073) at a temperature above roomtemperature. Room temperature is understood to be about 20° C. (68° F.);as such, the amorphous polycarbonate can be dissolved in the polaraprotic solvent at a temperature above about 20° C. The amorphouspolycarbonate is soluble in the polar aprotic solvent and thus apolycarbonate solution is formed. In general, the solution can beprepared at a temperature above room temperature so that the amount ofdissolved polycarbonate can be considered saturated at room temperature.Mixing of amorphous polycarbonate into the polar aprotic solvent can becarried out in-line or batch. The process can readily be carried out atmanufacturing scale. Upon cooling to room temperature (e.g., about 20°C.), the dissolved amorphous polycarbonate begins to crystallize andprecipitate out of the polar aprotic solvent resulting in theprecipitation of a partially crystalline polycarbonate precipitate. Itis further possible that when the precipitation occurs under high shearmixing conditions, the formation of an increased percentage ofcrystalline polycarbonate particles occurs while simultaneouslypreventing formation of firmly agglomerated polycarbonate particles. Ithas been found, for example, that agglomerates can be readily broken bycrushing, high speed mixing, or other low- or medium-force shearingprocesses.

Following precipitation, the polar aprotic solvent is removed and thepartially crystalline polymer powder can be dried by any suitable methodsuch as heating with or without vacuum or vacuum without heating. Theresulting crystalline polycarbonate powder can have a higher percentageof particles having a particle size greater than 10 μm and less than 150μm, as well as a relatively narrow particle size distribution. Therecovered solvent can be reused to begin the process anew by dissolvingadditional amorphous polycarbonate. This is unlike other methods thatuse one or more solvents that are mixed with non-solvents to precipitatecrystalline polycarbonate powder. Such mixtures of solvents andnon-solvents cannot be readily reused, but must be separated themselves.

As provided herein, amorphous polycarbonate is dissolved in a polaraprotic solvent. For example, the amorphous polycarbonate can bedissolved in the polar aprotic solvent under conditions that result in asaturated solution of polycarbonate, where changing conditions (e.g.,changing temperature of the solution) result in precipitation ofpartially crystalline polycarbonate powder therefrom. Typically, torealize a practical commercial process and to realize the desiredparticle size, shape and flowability, the concentration of thepolycarbonate in the polar aprotic solvent is at least about 5%, 10% or15% to about 30%, 25% or 20% by weight prior to precipitation.

In certain embodiments, the solvent can consist essentially of the polaraprotic solvent (e.g., diphenyl ether, anisole, DMSO, or the like),where no other components are present that materially affect thecrystallization of polycarbonate; e.g., no non-solvents are present, asdescribed by U.S. Pub. No. 2018/0244863. In certain embodiments, thesolvent can consist of the polar aprotic solvent, where there aresubstantially no other solvents present based upon the purity levelsattainable in the art with respect to that particular polar aproticsolvent. That is, the solvent can be substantially 100% polar aproticsolvent (e.g., DMSO, diphenyl ether, or anisole). It is further notedthat upon precipitating partially crystalline polycarbonate powder froma solution of polycarbonate and the polar aprotic solvent, a portion ofthe solubilized polycarbonate can remain in solution. Separation of theprecipitated partially crystalline polycarbonate powder from theremainder of the solution therefore leaves a solution of the polaraprotic solvent with a portion of solubilized polycarbonate that can bereused to again dissolve more amorphous polycarbonate. In the repeat useof the polar aprotic solvent (including the already dissolved portion ofpolycarbonate), less amorphous polycarbonate may need to be added toachieve a saturated state, for example, where changing from the firsttemperature to the lower second temperature results in anotherprecipitation of partially crystalline polycarbonate powder. Typically,the recovered yield of semi-crystalline polycarbonate from the processis 95% to 85% of the mass of amorphous polycarbonate dissolved in thesolution. Illustratively, it has been found that it is typical to have0.5% to about 5% by weight of polycarbonate remaining in a solution thathad been loaded to 20% by weight. These conditions have been found tocontribute to realizing the desired particle size and shape as describedbelow.

In certain embodiments, the partially crystalline polycarbonate powderhas a D₈₅ particle size of less than 150 μm, specifically, a D₉₀particle size of less than 150 μm. In certain embodiments, the partiallycrystalline polycarbonate powder has a D₉₅ particle size of less than150 μm, in which 95% of the partially crystalline polycarbonate powderhas a particle size of less than 150 μm. Certain embodiments includewhere the partially crystalline polycarbonate powder has a D₉₀ particlesize of less than 150 μm. A partially crystalline polycarbonate powderin which 100% of the particles have a size of less than 150 μm can alsobe produced by this method.

The partially crystalline polycarbonate powder can also have an averageparticle diameter of less than or equal to 100 μm. Specifically, thepartially crystalline polycarbonate powder can have an average particlediameter of 10 μm to 100 μm.

In certain embodiments, the partially crystalline polycarbonate powderhas a percent crystallinity of at least 20%, for example 20% to 80%,specifically, at least 25%, for example 25% to 60%, more specifically atleast 27%, for example 27% to 40%. The partially crystallinepolycarbonate powder can also have 25% to 30% crystallinity. Embodimentsfurther include 25% to 35% crystallinity.

In certain embodiments, a method of preparing an article comprisesproviding a powder composition comprising the partially crystallinepolycarbonate powder and using a powder bed fusing process with thepowder composition to form a three-dimensional object. The at least onepartially crystalline polycarbonate powder can have a D₅₀ particle sizeof less than 150 μm in diameter and is made by above-described methods.Embodiments include where the partially crystalline polycarbonate powderhas a D₉₀ particle size of less than 150 μm, an average particlediameter of less than or equal to 100 μm, and at least 20%crystallinity, or at least 25% crystallinity, or 25 to 35%crystallinity. The partially crystalline polycarbonate powder can bemade as described herein by converting an amorphous polycarbonate to thecrystalline polycarbonate powder. The conversion of the amorphouspolycarbonate includes dissolving the amorphous polycarbonate in asuitable polar aprotic organic solvent to form a solution above roomtemperature, cooling the solution to room temperature to form aprecipitate including partially crystalline polycarbonate powder,removing the solvent from the precipitate, drying the precipitate, andrecovering the crystalline polycarbonate powder.

The partially crystalline polycarbonate powder can be used as the solecomponent in the powder composition and applied directly in a powder bedfusing step. Alternatively, the partially crystalline polycarbonatepowder can first be mixed with other polymer powders, for example,another crystalline polymer or an amorphous polymer, or a combination ofa partially crystalline polymer and an amorphous polymer. The powdercomposition used in the powder bed fusing can include between 50 wt % to100 wt % of the partially crystalline polycarbonate powder, based on thetotal weight of all polymeric materials in the powder composition.

The partially crystalline polycarbonate powder can also be combined withone or more additives/components to make a powder useful for powder bedfusing methods. Such optional components can be present in a sufficientamount to perform a particular function without adversely affecting thepowder composition performance in powder bed fusing or the objectprepared therefrom. Optional components can have an average particlediameter which falls within the range of the average particle diametersof the partially crystalline polycarbonate powder or an optional flowagent. If necessary, each optional component can be milled to a desiredparticle size and/or particle size distribution, which can besubstantially similar to the partially crystalline polycarbonate powder.Optional components can be particulate materials and include organic andinorganic materials such as fillers, flow agents, and coloring agents.Still other additional optional components can also include, forexample, toners, extenders, fillers, colorants (e.g., pigments anddyes), lubricants, anticorrosion agents, thixotropic agents, dispersingagents, antioxidants, adhesion promoters, light stabilizers, organicsolvents, surfactants, flame retardants, anti-static agents,plasticizers a combination comprising at least one of the foregoing. Yetanother optional component also can be a second polymer that modifiesthe properties of the partially crystalline polycarbonate. In certainembodiments, each optional component, if present at all, can be presentin the powder composition in an amount of 0.01 wt % to 30 wt %, based onthe total weight of the powder composition. The total amount of alloptional components in the powder composition can range from greaterthan 0 up to 30 wt % based on the total weight of the powdercomposition.

It is not necessary for each optional component to melt during thepowder bed fusing process; e.g., a laser sintering process. However,each optional component can be selected to be compatible with thepartially crystalline polycarbonate polymer in order to form a strongand durable object. The optional component, for example, can be areinforcing agent that imparts additional strength to the formed object.Examples of the reinforcing agents include one or more types of glassfibers, carbon fibers, talc, clay, wollastonite, glass beads, andcombinations thereof.

The powder composition can optionally contain a flow agent. Inparticular, the powder composition can include a particulate flow agentin an amount of 0.01 wt % to 5 wt %, specifically, 0.05 wt % to 1 wt %,based on the total weight of the powder composition. In certainembodiments, the powder composition comprises the particulate flow agentin an amount of 0.1 wt % to 0.25 wt %, based on the total weight of thepowder composition. The flow agent included in the powder compositioncan be a particulate inorganic material having a median particle size of10 μm or less, and can be chosen from a group consisting of hydratedsilica, amorphous alumina, glassy silica, glassy phosphate, glassyborate, glassy oxide, titania, talc, mica, fumed silica, kaolin,attapulgite, calcium silicate, alumina, magnesium silicate, andcombinations thereof. The flow agent can be present in an amountsufficient to allow the partially crystalline polycarbonate polymer toflow and level on the build surface of the powder bed fusing apparatus(e.g., a laser sintering device). In certain embodiments the flow agentincludes fumed silica.

Another optional component is a coloring agent, for example a pigment ora dye, like carbon black, to impart a desired color to the object. Thecoloring agent is not limited, as long as the coloring agent does notadversely affect the composition or an object prepared therefrom, andwhere the coloring agent is sufficiently stable to retain its colorunder conditions of the powder bed fusing process and exposure to heatand/or electromagnetic radiation; e.g., a laser used in a sinteringprocess.

Still further additives include, for example, toners, extenders,fillers, colorants (e.g., pigments and dyes), lubricants, anticorrosionagents, thixotropic agents, dispersing agents, antioxidants, adhesionpromoters, light stabilizers, organic solvents, surfactants, flameretardants, anti-static agents, plasticizers, and combinations of such.

Still another optional component also can be a second polymer thatmodifies the properties of the partially crystalline polycarbonatepowder.

The powder composition is a fusible powder composition and can be usedin a powder bed fusing process such as selective laser sintering. Anexample of a selective laser sintering system for fabricating a partfrom a fusible powder composition, and in particular for fabricating thepart from the fusible crystalline polycarbonate powder disclosed herein,can be described as follows. One thin layer of powder compositioncomprising the partially crystalline polycarbonate powder is spread overthe sintering chamber. The laser beam traces the computer-controlledpattern, corresponding to the cross-section slice of the CAD model, tomelt the powder selectively which has been preheated to slightly belowits melting temperature. After one layer of powder is sintered, thepowder bed piston is lowered with a predetermined increment (typically100 μm), and another layer of powder is spread over the previoussintered layer by a roller. The process then repeats as the laser meltsand fuses each successive layer to the previous layer until the entireobject is completed. Three-dimensional objects comprising a plurality offused layers can thus be made using the partially crystallinepolycarbonate powder described herein.

The present technology provides certain benefits and advantages. Oneadvantage is the use of a single solvent in preparing the partiallycrystalline polycarbonate powder, which facilitates solvent recovery andreuse thereof. Another advantage is that amorphous polycarbonate can betransformed into a polycarbonate powder having crystallinity andoptimized particle size distribution for additive manufacturing. Yetanother advantage is that the partially crystalline polycarbonate powderprovides improved powder bed fusion performance. Additive manufacturingprocesses that employ fusion of a powder bed, including selective lasersintering (SLS), multi jet fusion (MJF), high speed sintering (HSS), andelectrophotographic 3D-printing, can therefore benefit by forming andusing partially crystalline polycarbonate powder produced as describedherein.

Process

An illustrative process of making pulverulent polycarbonate for additivemanufacturing and other applications may be comprised of the followingsteps: adding polycarbonate to a reactor vessel containing a suitablepolar aprotic organic solvent such as DMSO; an aromatic ether (e.g.,anisole or diphenyl ether); cyclic and cyclic ketones (e.g.,cyclopentanone, cyclohexanone, or acetophenone); acyclic and cyclicsecondary amides (e.g., N-methylpyrrolidinone (NMP) orN,N-dimethylformamide (DMF)); acyclic and cyclic esters (e.g.,γ-butyrolactone); or halogenated hydrocarbons (e.g., dichloromethane).

Additives may be mixed in, such as (e.g., inorganic oxide(s), organiccompounds, carbon microfibers, glass microfibers, and/or secondarypolymers) for the purpose(s) of particle nucleation, particledispersion, IR absorption, mineralization and strengthening, flameretardancy, and/or coloration; applying an inert atmosphere to thevessel. Desirably, the atmosphere is any, where the solvent and otherchemicals do not deleteriously react with the atmosphere. Generally, thedissolution is carried out at applied pressures at or near ambientpressures (e.g., ±10%, ±1% or ±0.1% of atmospheric pressure) in a closedvessel to minimize volatilization losses. The use of elevated pressuresmay be used but is not necessary. Exemplary atmospheres, depending onthe solvent may include nitrogen or noble gases (e.g., argon) orcombination thereof or air (e.g., dry air).

The mixture may be agitated during any portion of the method. Typically,the temperature is raised to facilitate the dissolution of thepolycarbonate. Desirably, the temperature, depending on the solvent, israised to at least about 100° C., 120° C., or 130° C. to about 180° C.,160° C., 150° C., 145° C. or 140° C. to fully dissolve the polycarbonateinto solution. Desirably, the peak operating temperature is below theboiling point of the solvent by at least 10° C. To facilitate theprecipitation and formation of desired particles, the solution is cooledto cause the polycarbonate to precipitate in powder form from thesolution. The polycarbonate powder may then be separated by any suitablemethod such as filtration, centrifugation, flotation or other knownmethod or combination thereof. The separation may be facilitated by oneor more additives such as solvents of lower molecular weight, surfaceactive agents, flotation enhancers and the like. In an embodiment, theseparation is performed by filtration (e.g., vacuum filtration) whichmay be facilitated by the addition of a solvent that is miscible withthe dissolving solvent and lowers the viscosity thereof at theseparating conditions or keeps the polar aprotic solvent from freezing(e.g., diphenyl ether) with examples being a low molecular weightorganic solvent such as a C₁ to C₄ alcohol.

The separated polycarbonate powder may be washed with a solvent (e.g.,water and/or a volatile organic solvent such as alcohol, ketone, ether,ester or hydrocarbon in which polycarbonate does not significantlydissolve) to remove the solvent in which the polycarbonate was dissolvedand precipitated. The separated polycarbonate with or without washingmay be dried by any suitable method such as those known in the art. Thedrying, for example performed by heating to any temperature useful forremoving any particular solvent. Illustratively, the temperature may beabove 60° C., 80° C., 100° C., 120° C., 140° C., to below the glasstransition temperature of the partially crystalline polycarbonate (e.g.,−155° C.), and preferably under reduced pressure. Desirably thetemperature is at least 10° C. below the glass transition temperature.

It is believed, without being limiting, that the presence of a polarsolvent exhibiting effective intermolecular interactions with the polarfunctional groups in the polycarbonate chains facilitates organizationof the polymer chains into crystalline domains in the precipitationprocess. Likewise, it is believed, that the cooling rate must beadequately slow to allow for the precipitation of solid semi-crystallinespheroidal polycarbonate powder particles, of a particle size sufficientto efficiently and effectively make articles by fusion bed additivemanufacturing techniques. Desirably, the cooling rate is at most about5° C./min, 4° C./min, 3° C./min, 2° C./min, 1° C./min to any practicalrate such 0.001° C./min from the dissolution temperature to thetemperature where the polycarbonate precipitates or to room temperatureor ambient temperature (˜15° C. to ˜30° C.).

Flowability herein means the flowability as determined by Method A ofASTM D 1895 using a 10 or 15 mm nozzle. Generally, the polycarbonatepowder has a flowability of at least about 0.5 g/s, 1 g/s or 2 g/s toany practically achievable rate (e.g., 50 g/s) using a 15 mm nozzle.

A variety of methods to chemically precipitate the above-identifiedpolymers may be employed. One skilled in the art will appreciate, basedon illustrative methods described below, that other precipitationmethods may be employed in the embodiments though they are notexplicitly disclosed herein.

The term “agitating the mixture” refers to methods of stirring thecomponents in a liquid or slurried mixture under conditions in whichshear forces are generated, creating patterns of flow and turbulence,generally using an impellor that rotates inside a stator. The stirringmay be any useful to realize a shear rate that results in the desiredparticle size and shape. Once the impellor has drawn mixture in, itsubjects the mixture to sudden changes of direction and accelerationsuch that the mixture contacts the wall of the stator with centrifugalforce, or is forced through the holes in the stator under pressure andspeed, in a final disintegrating change of direction and acceleration.In exemplary embodiments of high shear mixing conditions, mixingcomprises operating at speeds of 50 rotations per minute (rpm) to 500rpm. Agitation can be achieved with any commercially available mixers;for example, a mixer such as a Hei-Torque 200 reactor stirring motor canbe used.

It is appreciated that the rotation rate of the stirrer, precipitationtemperature, and time can be modified to potentially affect the particlesize of the resulting polycarbonate powder. It is also appreciated thatthe powder may be reprecipitated.

It is further appreciated that the polycarbonate may also be mixed indifferent ratios and particle sizes. This may have the effect ofchanging or controlling the properties of the resulting pulverulentpolycarbonate.

Melting point and enthalpy may be determined using differential scanningcalorimetry (DSC); for example, a TA Instruments Discovery Series DSC250.

Young's modulus of elasticity and tensile strength maybe determinedpursuant to the ASTM D 790 standard.

Scanning electron microscopy was performed using a JEOL instrumentoperating in low vacuum secondary electron detection (LVSED) mode.

The process for modifying the produced pulverulent polycarbonatematerial for additive manufacturing may comprise: adding at least onecompatible filler to the polycarbonate, wherein the fillers are eitherorganic or inorganic; at least one filler being selected from the groupconsisting of glass, metal, or ceramic particles, pigments, titaniumdioxide particles, and carbon black particles; particle size of at leastone filler being about equal to or less than particle sizes of thepolycarbonate; the particle sizes of at least one filler does not varymore than about 15-20 percent of an average particle size of thepolycarbonate; at least one filler is less than about 3% by weight ofthe polycarbonate; a flow agent being incorporated into the powderedpolycarbonate; the flow agent being selected from at least one of afumed silicas, calcium silicates, alumina, amorphous alumina, magnesiumsilicates, glassy silicas, hydrated silicas, kaolin, attapulgite, glassyphosphates, glassy borates, glassy oxides, titania, talc, pigments, andmica; the flow agent having a particle size of about 10 microns or less;the flow agent does not significantly alter the glass transitiontemperature of the polycarbonate; the flow agent is present in an amountless than about 5% by weight of polycarbonate.

Disclosed herein also are methods for powder bed fusing a powdercomposition, including the partially crystalline polycarbonate powder,to form a three-dimensional article. The spheroidal shape of the polymerpowder particles results in good flowability of the partiallycrystalline polycarbonate powder, and thus a smooth and dense powder bedcan be formed allowing for optimum precision and density of the sinteredpart. Also, the partially crystalline nature of the polymeric materialallows for ease of processing.

“Powder bed fusing” or “powder bed fusion” includes all laser sinteringand all selective laser sintering processes as well as other powder bedfusing technologies as defined by ASTM F2792-12a. For example, sinteringof the powder composition can be accomplished via application ofelectromagnetic radiation other than that produced by a laser, with theselectivity of the sintering achieved, for example, through selectiveapplication of inhibitors, absorbers, susceptors, or the electromagneticradiation (e.g., through use of masks or directed laser beams). Anyother suitable source of electromagnetic radiation can be used,including, for example, infrared radiation sources, microwavegenerators, lasers, radiative heaters, lamps, or a combination thereof.

Also included herein are all three-dimensional products made by powderbed fusing these powder compositions. After a layer-by-layer manufactureof an article of manufacture, the article can exhibit excellentresolution, durability, and strength. These articles of manufacture canhave a wide variety of uses, including as prototypes and as end productsas well as molds for end products.

In some embodiments of the methods, a plurality of layers is formed in apreset pattern by an additive manufacturing process. “Plurality”, asused in the context of additive manufacturing, includes five or morelayers, or twenty or more layers. The maximum number of layers can varygreatly, determined, for example, by considerations such as the size ofthe article being manufactured, the technique used, the capabilities ofthe equipment used, and the level of detail desired in the finalarticle.

As used herein, “layer” is a term of convenience that includes anyshape, regular or irregular, having at least a predetermined thickness.In some embodiments, the size and configuration of two dimensions arepredetermined, and on some embodiments, the size and shape of allthree-dimensions of the layer is predetermined. The thickness of eachlayer can vary widely depending on the additive manufacturing method. Insome embodiments, the thickness of each layer as formed differs from aprevious or subsequent layer. In some embodiments, the thickness of eachlayer is the same. In some embodiments the thickness of each layer asformed is 0.05 millimeters (mm) to 5 mm.

The preset pattern can be determined from a 3D digital representation ofthe desired article as is known in the art and described in furtherdetail below.

The fused layers of powder bed fused articles can be of any thicknesssuitable for selective laser sintered processing. The individual layerscan be each, on average, preferably at least 100 μm thick, more preferably at least 80 μm thick, and even more preferably at least 50 μmthick. In a preferred embodiment, the plurality of sintered layers areeach, on average, preferably less than 500 μm thick, more preferablyless than 300 μm thick, and even more preferably less than 200 μm thick.Thus, the layers for some embodiments can be 50 to 500 μm, 80 to 300 μm,or 100 to 200 μm thick. Three-dimensional articles produced from powdercompositions of the invention using a layer-by-layer powder bed fusingprocesses other than selective laser sintering can have layerthicknesses that are the same or different from those described above.

Powder-based 3D-printing includes a part bed and feed mechanism. Thispart bed is generally at a steady temperature before it is subjected toan energy source. That energy source is raised until a fusiontemperature is reached. The pulverulent polycarbonate may be placed in afeeder at a start temperature. During operation additional polycarbonateis placed on top of the original polycarbonate which cools and needs tobe raised again. It is believed that only the portion of polycarbonatethat is directly subjected to energy will be melted and not thesurrounding polycarbonate.

For purposes of this disclosure, an “operating window” is defined by thetypical range between the melting and the recrystallization (or glasstransition) temperatures. Semi-crystalline polycarbonates possess adefinitive melting point, allowing for the establishment of an operatingtemperature near the melting point of the polycarbonate in SLS, MJF,HSS, and possibly electrophotography 3D-printing applications. Thiswell-defined melting behavior allows for an operating window that keepsthe rest of the material unmelted, such as even in the presence of alaser or IR heater used during 3D-printing in solid form. The unmeltedsolid material can then act as a supporting structure for the moltenpolycarbonate.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms, and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail. Equivalent changes, modifications and variations ofsome embodiments, materials, compositions and methods can be made withinthe scope of the present technology, with substantially similar results.

The following Examples further illustrate the above concepts.

Example 1

An illustrative embodiment of the process for making pulverulentpolycarbonate suitable for additive manufacturing is as follows. To a5-L four-neck round-bottom flask fitted with an overhead stirrer wasadded 1 kg polycarbonate (Lupoy 1303EP-22, MW=ca. 38,000 Da) and 3 LDMSO (99.7%, Acros Organics). The solvent was sparged and the flaskflushed with a nitrogen atmosphere for 20 minutes. The mixture washeated with an electric mantle to 160° C. with stirring at a rate of 200rpm to yield a solution of polycarbonate in DMSO. The mantle was removedto allow the reactor temperature to cool at a rate of 1° C./min whilecontinuing to stir at 200 rpm. The polycarbonate precipitated betweenabout 70° C. and about 80° C. The thick slurry was removed from thereactor and poured into a 50 μm nylon mesh bag nested inside of a 100 μmnylon mesh bag of equivalent dimensions. The DMSO was separated bysqueezing the bags. The residual powder was washed 3×4 L of water: thefirst for 30 min., the second for 15 hrs., and the third for 4 hrs. Thepowder slurry was filtered and dried at 120° C. for 16 hrs., followed bysieving sequentially through 250 μm and 180 μm sieves.

Density and Flowability. Average bulk density of pulverulentpolycarbonate prepared in this embodiment was 0.42 g/cm³. Average tapdensity was 0.52 g/cm³ (average Hausner ratio=1.26, Carr's index 0.20).Flowability was determined using a cone with a 10 mm nozzle diameter,and has an average value of 2.58 g/sec.

Particle size, shape and distribution (PSSD). PSSD was determined inwater using a Microtrac S3500 instrument. D₉₀=67.8 μm; D₅₀=37.7 μm;D₁₀=16.8 μm. Circularity data is shown in Table 1:

TABLE 1 >0.65 97.03% >0.75 89.64% >0.85 64.43% >0.90 28.70% >0.95 7.01%

Molecular weight. GPC samples were prepared at a concentration of 2mg/mL tetrahydrofuran (THF), and are eluted at a flow rate of 1 mL/min.on a Waters GPC instrument with a Styragel HR4 5-μm 7.8×300 mm (THF)column and a 2414 Refractive Index Detector. The peak molecular weight(M_(P)) of the raw polycarbonate=38093 Da; M_(P) of pulverulentpolycarbonate=29900 Da.

Scanning Electron Micrography (SEM). SEM images reveal spheroidal,partially agglomerated particles of a typical size in agreement withPSSD results.

Differential Scanning calorimetry (DSC) and Crystallinity. The DSC wasperformed on a TA Instruments DSC 250 instrument scanning at 20° C./min.and is shown in FIG. 3 . Onset of melting occurred at 208.88° C., andpeaked at 236.39° C. Upon cooling, a glass transition appeared at 142°C., and again upon secondary heating at 147° C., after which no meltingbehavior was observed.

The percent crystallinity of semi-crystalline pulverulent polycarbonatewas estimated by measuring the enthalpy of fusion in the melting peak(31.407 J/g) and comparing it with the reference value for the enthalpyof fusion for 100% crystalline polycarbonate, reported as 134 J/g in theliterature (K. Varadarajan, et al., J. Polym. Sci. Polym. Phys. 1982,20(1), 141-154). The estimated crystallinity of semi-crystallinepolycarbonate of this example was therefore 23.4%.

SLS Printing of Pulverulent Polycarbonate. The pulverulent polycarbonatewas utilized in the laser sintering process on a Farsoon ST252P lasersintering system. Three kilograms of material was loaded into the feedpiston of the machine and settled into the piston achieving the optimaltapped density using a cement vibrator. Under an inert nitrogenatmosphere, material was moved from the feed piston to the part pistonin a layerwise fashion using a counter-rotating roller at layerthicknesses of 0.080 mm. Layers were laid at 90s intervals in order toallow for sufficient thermal absorption from near-IR heaters, duringwhich time the temperature of the feed piston ramped from 60° C. to 180°C. and the part bed temperature ramped from 60° C. to 207° C. Once thepart bed temperature reached the set point of 207° C., part areas wereexposed using the scanning system parameters shown in Table 2 in orderto melt selected areas into solid parts:

TABLE 2 Laser spot size (μm) 450 Fill scan speed (mm/s) 10,160 Fill scanspacing (mm) 0.28 Fill laser power (W) 30

Parts produced included thin discs, crosses, “window” test coupons, andASTM D638 Type IV tensile bars. Parts featured a slight yellow tint, butwere mostly translucent and lacked the opaque appearance of typicallaser sintering materials.

Example 2

An illustrative embodiment of the process for making pulverulentpolycarbonate suitable for additive manufacturing is as follows. To a20-L Reactor fitted with an overhead stirrer was added 4.0 kgpolycarbonate (Lexan 121R 112) and 15.73 L DMSO (99.7%, Acros Organics).The solvent was sparged and the flask flushed with an argon atmospherefor 4 hours. The mixture was heated with an oil jacket to 160° C. withstirring at a rate of 180 rpm to yield a solution of polycarbonate inDMSO. The reactor was allowed cool at a rate of 0.1-0.2° C./min whilecontinuing to stir at 180 rpm. The polycarbonate precipitated betweenabout 70° C. and about 80° C. The thick slurry was removed from thereactor and poured into a 50 μm nylon mesh bag nested inside of a 100 μmnylon mesh bag of equivalent dimensions. The DMSO was separated bysqueezing the bags. The residual powder was soaked in 1×30 L of waterfor 3 days. This was removed by using the aforementioned bags. Theresidual powder was soaked in 1×10 L of Methanol for 2 hours andseparated using 5 μm filter paper in a 20 L vacuum filter.

The powder was dried at 120° C. for 33 hrs., followed by sievingsequentially through 250 μm and 180 μm sieves.

Particle size and distribution (PSD). PSD was determined in air using aMicrotrac S3500 instrument. D₉₀=22.48 μm; D₅₀=14.96 μm; D₁₀=10.93 μm.

Differential Scanning calorimetry (DSC) and Crystallinity. The DSC wasperformed on a TA Instruments DSC 250 instrument scanning at 20° C./min.and is shown in FIG. 3 . Onset of melting occurred at 207.56° C., andpeaked at 241.28° C.

The percent crystallinity of semi-crystalline pulverulent polycarbonatewas estimated by measuring the enthalpy of fusion in the melting peak(31.377 J/g) and comparing it with the reference value for the enthalpyof fusion for 100% crystalline polycarbonate, reported as 134 J/g in theliterature (K. Varadarajan, et al., J. Polym. Sci. Polym. Phys. 1982,20(1), 141-154). The estimated crystallinity of semi-crystallinepolycarbonate was therefore 23.4%.

SLS Printing of Pulverulent Polycarbonate. The pulverulent polycarbonatewas utilized in the laser sintering process on a Farsoon ST252P lasersintering system. Two- and one-half kilograms of material was loadedinto the feed piston of the machine and settled into the pistonachieving the optimal tapped density using a cement vibrator. Under aninert nitrogen atmosphere, material was moved from the feed piston tothe part piston in a layerwise fashion using a counter-rotating rollerat layer thicknesses of 0.061 mm. Layers were laid at 90s intervals inorder to allow for sufficient thermal absorption from near-IR heaters,during which time the temperature of the feed piston ramped from 60° C.to 180° C. and the part bed temperature ramped from 60° C. to 207° C.Once the part bed temperature reached the set point, it was lowered to205.5° C. as the part bed started to crack, part areas were exposedusing the scanning system parameters shown in Table 3 in order to meltselected areas into solid parts:

TABLE 3 Laser spot size (μm) 450 Fill scan speed (mm/s) 10,160 Fill scanspacing (mm) 0.20 Fill laser power (W) 60 Number of scans 3 Layerinterval (s) 23

Parts produced included thin discs, crosses, “window” test coupons, andASTM D638 Type IV tensile bars. Parts featured a slight yellow tint, butwere mostly translucent and lacked the opaque appearance of typicallaser sintering materials.

Example 3

An illustrative embodiment of the process for making pulverulentpolycarbonate suitable for additive manufacturing is as follows. To a20-L Reactor fitted with an overhead stirrer was added 3.21 kgpolycarbonate (Lupoy 1080C 70, MW=ca. 30,000 Da) and 13.76 L DMSO(99.7%, Acros Organics) [A second batch consisting of 3.00 kgpolycarbonate (Lupoy 1080C 70) and 12.96 L DMSO (99.7%, Acros Organics)was performed alongside this one]. The solvent was sparged and thereactor flushed with an argon atmosphere for 3 hours. The mixture washeated with an oil jacket to 160° C. with stirring at a rate of 180 rpmto yield a solution of polycarbonate in DMSO. The reactor was allowedcool at a rate of 0.1-0.2° C./min while continuing to stir at 180 rpm.The polycarbonate precipitated between about 70° C. and about 80° C. Theslurry was removed from the reactor, combined with the second batch, andpoured into a 20 L vacuum filter flask with a 4 μm filter paper. 15 L ofDMSO was recovered using this method. The residual powder was processedusing 140 L of DI water and 20 L of acetone as follows: soaked in 2×15 Lof water for 1 day; filtered and soaked with 1×25 L of water for 1 day;filtered, washed with 2×20 L of water, and soaked in 25 L of water for 1day; filtered, washed with 1×20 L of water and 1×20 L of acetone. Thepowder was dried at 110° C. for 72 hrs., followed by a 250 μm sieveproviding 4.5 kg of powder.

Density and Flowability. Average bulk density of pulverulentpolycarbonate prepared in this embodiment was 0.42 g/cm³. Average tapdensity was 0.48 g/cm³ (average Hausner ratio=1.15, Carr's index 0.12).Flowability was determined using a cone with a 15 mm nozzle diameter,and has an average value of 8.93 g/sec.

Particle size distribution (PSD). PSD was determined in air using aMicrotrac S3500 instrument. D₉₀=101.5 μm; D₅₀=69.56 inn; D₁₀=45.69 inn.

Molecular weight. GPC samples were prepared at a concentration of 2mg/mL tetrahydrofuran (THF), and are eluted at a flow rate of 1 mL/min.on a Waters GPC instrument with a Styragel HR4 5-μm 7.8×300 mm (THF)column and a 2414 Refractive Index Detector. The peak molecular weight(M_(P)) of the raw polycarbonate=30318 Da.

Scanning Electron Micrography (SEM). SEM images reveal spheroidal,partially agglomerated particles of a typical size in agreement with PSDresults.

Differential Scanning calorimetry (DSC) and Crystallinity. The DSC wasperformed on a TA Instruments DSC 250 instrument scanning at 20° C./min.and is shown in FIG. 3 . Onset of melting occurred at 196.67° C., andpeaked at 233.97° C. Upon secondary heating, a glass transition occurredat 138.84° C., after which no melting behavior was observed.

The percent crystallinity of semi-crystalline pulverulent polycarbonatewas estimated by measuring the enthalpy of fusion in the melting peak(31.407 J/g) and comparing it with the reference value for the enthalpyof fusion for 100% crystalline polycarbonate, reported as 134 J/g in theliterature (K. Varadarajan, et al., J. Polym. Sci. Polym. Phys. 1982,20(1), 141-154). The estimated crystallinity of semi-crystallinepolycarbonate was therefore 26.9%.

SLS Printing of Pulverulent Polycarbonate. The pulverulent polycarbonatewas utilized in the laser sintering process on a Farsoon ST252P lasersintering system. Four and one half kilograms of material was loadedinto the feed piston of the machine and settled into the pistonachieving the optimal tapped density using a cement vibrator. Under aninert nitrogen atmosphere, material was moved from the feed piston tothe part piston in a layerwise fashion using a counter-rotating rollerat layer thicknesses of 0.102 mm. Layers were laid at 90s intervals inorder to allow for sufficient thermal absorption from near-IR heaters,during which time the temperature of the feed piston ramped from 60° C.to 200° C. and the part bed temperature ramped from 60° C. to 219° C.Once the part bed temperature reached the set point of 219° C., partareas were exposed using the scanning system parameters shown in Table 4in order to melt selected areas into solid parts:

TABLE 4 Laser spot size (μm) 450 Fill scan speed (mm/s) 10,160 Fill scanspacing (mm) 0.20 Fill laser power (W) 35 Number of scans 2 Layerinterval (s) 30

Parts produced included thin discs, large cubes, and ASTM D638 Type IVtensile bars. Parts featured a slight yellow tint, but were mostlytranslucent and lacked the opaque appearance of typical laser sinteringmaterials.

Example 4

30 g of Lexan 121 polycarbonate was dissolved in 100 mL of acetophenone.The mixture was placed in a 300 mL Erlenmeyer flask and stirred andheated on a magnetic hot plate to 182° C. At this temperature, thepolycarbonate was observed to be fully dissolved. The heater was turnedoff and the solution was allowed to cool while stirring. The solutionwas visually cloudy when observed at approximately 52° C. The solutionwas held at ambient conditions (approximately 20° C.) overnight, forapproximately 15 hours. 200 mL of acetone was added to thin out thesolution before filtering via vacuum filtration. The solids that wereseparated from the solution were dried by placing them in a ventilatedlab hood overnight.

Example 5

In a 250 mL Erlenmeyer flask, 24 g of Iupilon E2000UR PC and 100 mL ofdiphenyl ether were added along with a magnetic stir bar. The sample washeated to 140° C. with continuous stirring. Once the pellets hadcompletely dissolved, the solution was allowed to cool to roomtemperature overnight and precipitate powder. The precipitated powderwas then broken up, placed in a 500 mL beaker, covered with 200 mL ofIPA, capped with foil, and allowed to wash for 1 hour. It was thenfiltered and dried in a 130° C. conventional oven.

Differential Scanning calorimetry (DSC) and Crystallinity. The DSC wasperformed on a TA Instruments DSC 250 instrument scanning at 20° C./min.The glass transition upon heating occurred with a midpoint of 151.39° C.Onset of melting occurred at 222.36° C. and peaked at 256.00° C. with anenthalpy of fusion of 38.084 J/g, representative of a powder with 28.4%crystalline character. Upon cooling, no noticeable recrystallizationpeak appeared; however, the glass transition appeared again uponcooling, with a midpoint of 147.05° C.

Example 6

In a 250 mL Erlenmeyer flask, 24 g of Iupilon E2000UR PC and 111 mL ofanisole were added along with a magnetic stir bar. The sample was heatedto 140° C. with continuous stirring. Once the pellets had completelydissolved, the solution was allowed to cool to room temperatureovernight and precipitate powder. The precipitated powder was thenbroken up, placed in a 500 mL beaker, covered with 200 mL of IPA, cappedwith foil, and allowed to wash for 1 hour. It was then filtered anddried in a 130° C. conventional oven.

1. A method of preparing a partially crystalline polycarbonate powder,the method comprising: dissolving an amorphous polycarbonate in a polaraprotic solvent to form a first solution of solubilized polycarbonate ata first temperature; and cooling the first solution to a secondtemperature, the second temperature being lower than the firsttemperature, wherein a portion of the solubilized polycarbonateprecipitates from the first solution to form a slurry comprised of thepartially crystalline polycarbonate powder and a less-than-saturated orsaturated solution of the polycarbonate, wherein the second temperatureis room temperature.
 2. The method of claim 1, further comprisingseparating the partially crystalline polycarbonate powder from theslurry.
 3. The method of claim 2, wherein, prior to or during theseparating, a low molecular weight miscible solvent that does notdissolve the polycarbonate is added to the slurry.
 4. The method ofclaim 3, wherein the low molecular weight miscible solvent is a C₁ to C₄alcohol and the separation is performed using filtration.
 5. The methodof claim 1, further comprising repeating the dissolving step using theremainder of the second solution as the polar aprotic solvent andrepeating the cooling step to form the second solution including anotherpartially crystalline polycarbonate powder, wherein at least a portionof the polycarbonate dissolved is leftover from the prior dissolving andprecipitating.
 6. The method of claim 1, wherein the polar aproticsolvent is comprised of one or more of the following: dimethylsulfoxide; diphenyl ether; or anisole.
 7. The method of claim 1, whereinthe polar aprotic solvent consists essentially of one of the following:dimethyl sulfoxide; diphenyl ether; or anisole.
 8. The method of claim1, wherein the dissolving step includes heating the amorphouspolycarbonate in the polar aprotic solvent to form the first solution ofsolubilized polycarbonate at the first temperature, the firsttemperature being greater than room temperature.
 9. The method of claim8, wherein the cooling step includes cooling the first solution to thesecond temperature at a cooling rate, the second temperature being roomtemperature and the cooling rate being at most about 5° C./min.
 10. Themethod of claim 1, wherein the first solution is saturated withamorphous polycarbonate at the first temperature.
 11. The method ofclaim 1, wherein the partially crystalline polycarbonate powder has aD₉₀ particle size of less than about 150 μm and a D₁₀ of at least 10 μm.12. (canceled)
 13. The method of claim 11, wherein the partiallycrystalline polycarbonate powder has an average particle diameter fromabout 30 μm to about 40 μm.
 14. The method of claim 13, wherein thepartially crystalline polycarbonate powder has at least about 90% of theparticles by number having a circularity of 0.65 or greater. 15.(canceled)
 16. The method of claim 14, wherein the partially crystallinepolycarbonate powder has a crystallinity of about 25% to about 35%. 17.(canceled)
 18. (canceled)
 19. (canceled)
 20. (canceled)
 21. (canceled)22. (canceled)
 23. The method of claim 1, wherein the concentration ofthe polycarbonate in the first solution is about 5% to about 30% byweight.
 24. (canceled)
 25. The method of claim 1, wherein the firsttemperature is from about 100° C. to 150° C.
 26. The method of claim 25,wherein the first temperature is at most about 145° C.
 27. The method ofclaim 1, wherein the dissolving and cooling are carried out under apressure within 1% of atmospheric pressure.
 28. The method of claim 27,wherein the dissolving and cooling are carried out under an inertatmosphere.